Field
The present application relates to a bistable electromagnetic actuator, such as for use in a surgical instrument, comprising a stator arranged outside of a tube, and a rotor mounted in the tube so as to be displaceable along the longitudinal axis, the rotor at least partially comprises a paramagnetic and/or ferromagnetic material and can be reversibly displaced between a first position and a second position by applying an electromagnetic field, wherein the stator comprises two, which can be oppositely axially poled, ring permanent magnets, a coil for producing the electromagnetic field, and a back-iron element having two stator pole shoes; as well as a surgical instrument.
Prior Art
Bistable electromagnetic actuators have a rotor that is held in one of two extreme positions in a permanent magnetic field, and can be moved out of one stable position into the other stable position by switching an electromagnetic field. This can for example actuate switches. In the case of surgical instruments, such as endoscopes, these compact actuators can be used for example to change a focus or enlarge an optical system, or to change a direction of viewing. This is accomplished in that an optical component is moved by the actuator, wherein the optical component is located in or on the rotor of the actuator.
A linear motor for optical systems such as endoscopes is known from DE 10 2008 042 701 A1. The motor has a stator with two permanent magnets which are polled in the same direction and magnetically connected to each other with a back-iron element. A coil is arranged between the magnets. On the side next to each magnet, a pole shoe is magnetically connected to the back-iron element. The motor rotor comprises a yoke consisting of a soft magnetic material that magnetically engages with the permanent magnet of the stator. By supplying current to the coil, the rotor can be moved in the longitudinal direction from a resting position.
The rotor according to DE 10 2008 042 701 A1 consists of a tubular, soft magnetic element so that a strong force must be expended to move the rotor from one position into the other position due to the resulting friction of the tubular rotor against the tube. Furthermore, the linear motor according to DE 10 2008 042 701 A1 is comparatively large.
Conventional actuators use permanent magnets that can also be designated permanent magnet rings, for example consisting of magnetic materials such as NdFeB or SmCo. These magnetic materials are brittle and therefore very sensitive to mechanical loads. With endoscopes, it is additionally desirable to use minute magnets and small outer diameters. This makes the production of the ring permanent magnet very involved. In addition, the ring permanent magnets are very easy to damage when being installed and must be specially protected even in an installed state to prevent damage.
Furthermore, it is important to use two ring permanent magnets that only have a minor dimensional deviation from each other since otherwise an excessive deviation in symmetry can arise in the actuator which for example can produce malfunctioning or poor functioning of the actuator. For example in one of the bistable positions, less holding force can arise on one side than in the other bistable position, which may not be desirable. This can be avoided by sorting conventional ring permanent magnets into pairs that, for example, are manufactured by sintering and then ground to size in order for example to install if possible magnets with the same dimensions and the same magnetic properties in an endoscope.